High-power direct current engine comprising a collector and carbon brushes for a racing car serving as prototype

ABSTRACT

A DC motor includes a rotor which is mounted in a housing so that it can rotate about an axis. The rotor includes at least one winding to which direct current is applied from the outside in alternating directions via a commutator, which is arranged on the rotor. Brushes are seated on the commutator and are mounted whereupon they can move relative to the commutator while being pushed by spring pressure onto the commutator.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to the field of DC motor technology. Itrelates in particular to a high-power DC motor, especially for modelracing vehicles.

2. Prior Art

Small, extremely high-power DC motors which rotate at a high speed areused nowadays for driving battery-powered model racing cars, model boatsor model aircraft. Examples of such high-power DC motors for modelracing cars are the RC2140 or RC2141 types from the American companyTrinity Products, Inc. Edison, N.J. (USA), or the “Chrome Touring”series of motors from the Swiss company Team Orion Europe SA, 1233Bernex, Switzerland. FIG. 1 shows an example of the design of such DCmotors from the prior art in simplified form and in the form of adetail, with the figure element 1A showing a longitudinal sectionthrough the motor and the figure element 1B showing a plan view in theaxial direction of the motor head. The DC motor 10 shown in FIG. 1 has ahousing 16 with magnets 17 (the fixed part) which are arranged on theinside, and in which a rotor 11 (the rotating part of the motor) ismounted such that it can rotate about an axis 29. The rotor 111comprises a central shaft 15, an armature 12 with appropriate windings13 and a commutator 14 (for the sake of simplicity, only one of thewindings is shown).

The armature 12 is composed, in a known manner, of a material with highmagnetic permeability. An electrical current flows through the windings13, producing a magnetic field when the DC motor 10 is supplied withcurrent, and with this magnetic field interacting with the magnets(permanent magnets) 17 on the housing 16. The commutator 14 is composedof individual electrically conductive commutator segments 20, normallymade of metal, which are isolated from one another and are arranged on acylindrical casing surface about the axis 29. The commutator segments 20are electrically connected to the windings 13 via winding connections 18in a predetermined manner. The commutator controls the time duration anddirection of the current flow through the windings 13, such that theattraction and repulsion forces cause the rotor 11 to rotate dependingon the magnetic field direction in the armature 12 and on the polarityof the magnets 17.

The housing 16 of the DC motor 10 is provided at both ends with slidingbearings, ball bearings 21 or similar bearings, which guide the centralshaft 15 of the rotor 11. Furthermore, brush boxes 24 which extend inthe radial direction and in which brushes 22, 23 are guided are arrangedon opposite sides in the motor head 19 in which the commutator 14 isaccommodated. Brushes 22, 23 may be composed of carbon. However, theymay also be composed of a material other than carbon, in particular andalso including a material mixture, for example of carbon, graphite,copper, silver or the like. The inner ends of the brushes 22, 23 areseated on the commutator 14 and in this way guide the current from therigid part of the motor via the commutator 14 to the windings 13 of therotor 11. The brushes 22, 23 are pressed against the commutator 14 bypressure springs 27, and are electrically conductively connected viacurrent-carrying braids 25 to electrical connecting poles 26.

During operation of the DC motor 10, centrifugal forces act on the rotorand generally lead to the central shaft 15 no longer rotating centrally.The radial gap between the central shaft 15 of the rotor 11 and thebearings, in particular the gap in the ball bearings 21 allows the axisof the rotor 11 to be shifted radially and the rotor 11 not to rotateroundly. When sliding bearings are used, the gap increases as thesliding bearings wear.

Dynamic balancing of the rotor 11 only partially improves the situation.The shifting of the centre can also be caused by unequal magneticforces. The drive force of the motor when the motor is installed istransmitted to other rotating parts. When power is drawn, a lever effectis produced which forces the rotor 11 against the bearing walls. Thelever effect can become even greater during acceleration and braking.These forces vary over the course of operation of the motor and forcethe rotor 11 away from the ideal centre.

The uncentred rotation of the shaft 15 of the rotor 11 results in thecommutator 14 not rotating centrally either, that is to say not runningroundly. The brushes 22, 23 are forced against the commutator segments20 by pressure springs 27. Thus, when the rotor 11 is not runningroundly, the brushes 22, 23 have to follow the backward and forwardmovement of the commutator 14. At low rotation speeds, the brushes 22,23 can follow this by moving backward and forward in the movementdirection 28 in their brush boxes 24 (FIG. 1B), so that the contactbetween the brushes 22, 23 and the commutator segments 20 is alwaysgood.

However, as soon as the rotation speed rises, the brushes 22, 23 areknocked away in the movement direction 28 by the commutator 14, lift offthe commutator 14 and do not make contact with the next commutatorsegment 20 again until later. The electrical contact is made with a timedelay, and the power of the motor falls.

If the brushes 22, 23 do not slide smoothly from one commutator segment20 to the next, the electrical contact is interrupted at times. Theinterruption and the renewed making of the contact lead to sparks beingformed between the brushes 22, 23 and the commutator segments 20. Thesesparks burn the commutator segments 20. The commutator segments 20 aredamaged, and the quality of the current transmission suffers and falls.The commutator 14 is worn away prematurely, and the power of the motordecreases permanently. The sparks and the damaged commutator segments 20also increase the wear rate of the brushes 22, 23, and overheat them.

Sparks also form a heat source, so that the commutator segments aredeformed and are worn away irregularly. This adversely affects the lifeof the motor, and reduces its power.

The sparks also cause radio interference and can interfere with remotecontrol receiving systems, or even make them unusable, when motors suchas these are operated in the vicinity of radio receivers.

It is already known from WO-A1-01/69760 or JP-A-07-194067 for thebackward and forward movements of the brushes to be damped by using adamping substance (for example a thixotropic material) to guide thesprings, which also move. It is also known for the movement of thebrushes to be braked by mechanical friction, by a leaf spring pressingagainst the side of the brushes. Both the damping and the braking aresymmetrical, that is to say they are of equal intensity in both movementdirections of the brushes. Both the movement of the brushes away fromthe commutator and the movement of the brushes in the direction of thecommutator are thus damped or braked. This damping (braking) thus delaysthe time at which contact is next made between the brushes and thecommutator segments. No improvements can be achieved in this way. Whatis obtained on the one hand (when the brushes are lifting off thecommutator) is made worse on the other hand (when the brushes are movingtowards the commutator).

Furthermore, the current is normally passed via a current transmissionbraid (25 in FIG. 1B), which is fixed in the brush, to the brushes, andthen through the brush to the commutator. Overall, this forms anelectrical resistance. If this electrical resistance could be reduced,then the motor would produce more power The known solutions for dampingand braking the backward and forward movement of the brushes do notallow any improvements whatsoever with regard to reducing the magnitudeof the resistance.

U.S. Pat. No. 2,991,379 and the parallel DE-B-1 122 625 describe a brushholder for a servomotor, in which the longitudinal axes of the brushesin the brush boxes form an angle of about 45° with the motor axis. Inorder to avoid increased wear on the brushes and to achieve increasedno-load rotation speeds without having to increase the brush pressure,it is proposed that the brushes be guided better in the brush boxes. Forthis purpose, according to one embodiment (FIG. 1), the brush boxes aredesigned to have a polygonal (square, hexagonal) cross section, suchthat the motor axis lies on the plane which passes through two oppositeedges of the brush boxes. The brushes have a correspondingcross-sectional shape and are guided by two opposite longitudinal edgesin the grooves formed by the corners in the brush holders. The use ofthe edges of the brushes for guidance results in a greatly reducedcontact area between the brushes and the brush boxes, which on the onehand prevents effective friction damping of the brush movement, and onthe other hand makes it more difficult to supply current to the brushtip via the brush box.

In a second embodiment of U.S. Pat. No. 2,991,379 (FIG. 2), the brush isguided in a guide element which is open on one side, is in the form of arail and has a cross section in the form of a right angle. The springwhich provides the brush with pressure is inclined with respect to thelongitudinal axis of the guide element such that the brush is forcedinto the guide element, which is in the form of a groove, not only bythe commutator forces but also by the opposing spring forces. Thisadmittedly results in increased friction damping, but the frictiondamping is independent of the movement direction of the brushes.

U.S. Pat. No. 5,696,418 describes an electrical commutator machine inwhich the two brushes are arranged offset from the radial direction withrespect to the machine axis. A special mounting is proposed for thebrush boxes on a plate which surrounds the machine axis and is at rightangles to the machine axis. The brush boxes, which are bent from sheetmetal, have a rectangular cross section and are inserted intocorresponding slots in the plate, and are secured, by means of lugswhich project at right angles on the lower face. A spring tongue isformed (FIGS. 5, 6) in one side wall of the brush box, presses on theone side against the brush which is located in the brush box, and thuspresses this against the opposite wall of the brush box. This pressuremechanism not only results in the brush being fixed in the box but alsoresults in uniform friction on the opposite wall, which is independentof the movement direction of the brush.

Finally FR-A-2 723 481 discloses a brush holder for reversiblecommutator machines, in which two pairs of brush boxes are provided,which are each arranged offset from the radial direction with respect tothe motor axis. The brush holder is produced from a plastic, as aninjection-moulded part. The individual brush boxes have a square crosssection and are provided at the corners with rails (42) which projectinwards and in which the brushes are guided by their edges. The use ofplastic for production of the holder and the specific nature of the edgebearing mean that the holder is not suitable for use in high-powermotors, because the heat which is produced on the commutator cannot beeffectively dissipated in the brushes, because the current cannot bepassed directly into the front part of the brush and because thisresults in only a small amount of friction damping for the moving brush.

The solution to the problems which occur with the brushes in high-powerDC motors for model racing cars is made very much worse by the fact thatthe existing regulations (for racing operation) mean that the motors areon the one hand subject to major restrictions with regard to thegeometry (external dimensions) and electrical and mechanical design, andon the other hand have to achieve extreme power levels (rotation speed,acceleration time, torque, etc) at least over time periods of severalminutes. The motors can in this case reach rotation speeds of up to 60000 rpm, and draw a current of up to 120 A from the battery orrechargeable battery set, which is likewise subject to restrictions. Themotor heads in which the brushes are arranged may in this case be heatedup to 100° C. In the extreme, the brushes last for only a single race,which is only 5.5 minutes.

Racing with model racing cars which are driven electrically is subjectto internationally applicable laws, the so-called ROAR (RemotelyOperated Auto Racers) Rules, which specify, inter alia, the restrictionsand boundary conditions applicable to electrical drives. The ROAR rulesstate that the motor must not have an external diameter of more than36.02 mm and must not have a length of more than 53 mm, measured fromthe mounting plate at one end to the outermost point of the motor head.The diameter of the central shaft must be {fraction (1/8)} inch. Onlyceramic magnets are allowed. The commutator may have only three sectors.In the same way, a specific number of turns are specified. Based onspecific basic motor types, technical changes may be made to the motorswithin the rules, with such changes having a different scope dependingon the motor class. In this case, a distinction is drawn betweenso-called stock motors, rebuildable stock motors, and modified motors.The most extensive changes which also include, in particular, changes tothe brushes and to the internal design of the motor, may be made in thelast-mentioned motor class. However, owing to the extreme spacerestriction, the brushes can be modified only with major difficulties.

SUMMARY OF THE INVENTION

The invention is a high-power DC motor with a commutator and brushes formodel racing vehicles, in particular model racing cars, which avoids thedisadvantages of known DC motors and, in particular, counteracts areduction in the motor power owing to the movement of the brushes athigh rotation speeds, and at the same time allows the electricalresistance in the power supplies to the commutator to be reduced.

The essence of the invention is to introduce means by which the movementof the brushes against the spring pressure is damped or braked, whilethe movement of the brushes with the spring pressure remains largelyuninfluenced. This prevents or suppresses the brushes being knocked awayby the rotating commutator segments while, once a brush has been knockedaway, it is moved back again into contact with the commutator segmentsquickly, by the spring pressure, without any impediments.

One embodiment of the invention is characterized in that the brushes areeach mounted in brush boxes such that they can slide in a movementdirection which is predetermined by the brush boxes, and in that themovement direction of the brushes deviates from the radial directionwith respect to the axis in such a way that the brushes in their brushboxes are subjected to increased sliding friction on at least one wallof the brush boxes during movement against the spring pressure caused bythe commutator. When the commutator is exerting a repulsion force on thebrushes, the brushes are pressed against the at least one wall of thebrush boxes, owing to the oblique position of the brush boxes, and theirmovement in the box is impeded (braked, damped) by increased friction onthe at least one wall. When the repulsion forces ends, the brushes arepressed back against the commutator by the spring force of the pressuresprings without any traceable wall friction occurring.

The movement directions of the brushes each preferably include an angle(α) in the range between 15° and 75° with the radial direction withrespect to the axis. In particular, the angle (α) is about 45°.

In a first alternative, the movement directions of the brushes lie on acommon plane which passes through the axis of the DC motor. Inparticular, good accessibility to the brushes is in this contextachieved in that the movement directions of the brushes are alignedobliquely outwards.

In a second alternative, the movement directions of the brushes lie on acommon plane which is at right angles to the axis of the DC motor.

The design is particularly simple in this case if two brushes areprovided and are arranged with respect to one another such that they canbe transferred into one another by rotation through 180° about the axisof the DC motor.

A reduction in the resistance for the power supply and thus animprovement in the motor power is achieved in conjunction with increasedfriction on the brush boxes in that the walls of the brush boxes arecomposed of an electrically highly conductive material, in particular ofa metal. The brush boxes form an electrically highly conductive bypassfor the current, which can thus be passed with a reduced resistancedirectly to the tips of the brushes, which are seated on the commutator.It is particularly advantageous for the brush boxes to be conductivelyconnected to appropriate apparatuses for supplying electrical current.It is particularly advantageous with regard to heat dissipation and theelectrical supply for the walls of the brush boxes to be produced fromcopper.

The heat which is produced in the area of the commutator and of thebrushes can be dissipated particularly quickly and reliably by the brushboxes being arranged in a motor head in the form of a shell, in that themotor head is made of a thermally highly conductive material, inparticular of a metal, and in that the brush boxes are mounted in anelectrically isolated manner in the motor head. It is particularlyadvantageous from the design point of view and on the basis of thermalaspects for the motor head to be composed of aluminium and for the brushboxes to be electrically isolated from the motor head by an anodizedintermediate layer.

A further improvement in the heat dissipation can be achieved by themotor head having cooling ribs on the outer face, in order to improvethe heat emission to the environment, with the cooling ribs preferablybeing formed concentrically with respect to the axis of the DC motor.

In addition to passive heat dissipation via the motor head and the brushboxes, effective active cooling can be achieved by providing ventilationchannels in the motor head for supplying cooling air into the interiorof the DC motor, by the winding of the DC motor being electricallyconductively connected to the commutator via winding connections, withthe winding connections being designed such that they act as fan vaneswhen the motor is running in the normal direction and suck in coolingair through the ventilation channels, and by the ventilation channelsbeing in the form of helical lines.

In order to ensure that the rotor is borne precisely in an automaticallyadjusting manner and in order in this way to advantageously influencethe formation of sparks on the commutator, it is advantageous for thecentral shaft (at the end at which the commutator is located) of therotor to be mounted in a ball bearing such that it can rotate, and forthe ball bearing itself to be mounted elastically. This is preferablydesigned such that the ball bearing is mounted elastically in the radialand axial directions, and such that the elastic bearing is produced bymeans of O rings which concentrically surround the ball bearing on theoutside on the one hand, and are used to support the ball bearing in theaxial direction on the other hand.

The assembly process is particularly simple, with improved springcharacteristics at the same time, if pressure springs in the form ofspiral springs which taper conically towards the brushes are provided inorder to produce the spring pressure on the brushes, if the pressuresprings are supported by their ends facing away from the brushes on anundercut in the brush boxes, and if the pressure springs are made of anINOX wire.

When the current levels to the motor are high, it is desirable for thecable runs for the current to be as short as possible, in order tominimize losses. This can be achieved in that the brush boxes each havean apparatus to which all of the lines coming from the outside for therespective pole can be electrically connected. The apparatus forconnection of the lines which come from the outside is preferably in theform of a flange which surrounds the brush box and is preferablysubdivided into two or more sectors.

The sparks which occur on the commutator form a radio interferencesource. In order to ensure effective suppression despite the confinedspatial conditions for the model motor, a printed circuit board isarranged in the interior of the motor head and has a circuit for motorsuppression, and the circuit board is electrically conductivelyconnected to the brush boxes via contact springs which press against thebrush boxes. In addition, an externally visible light-emitting diode maybe arranged on the circuit board in order to check the rotationdirection of the motor.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail in the following textwith reference to exemplary embodiments and in conjunction with thedrawings, in which:

FIGS. 1A and 1B show a DC motor with a commutator and brushes accordingto the prior art, in a longitudinal section and a plan view from thefront, respectively;

FIGS. 2A and 2B show a longitudinal section and a plan view,respectively, of a DC motor according to a first embodiment of theinvention;

FIG. 3 shows the brush arrangement from FIG. 2A, in an enlarged detailedview;

FIGS. 4A and 4B show a longitudinal section and a plan view,respectively, of a DC motor according to a second embodiment of theinvention;

FIG. 5 shows the brush arrangement from FIG. 4B, in an enlarged detailedview;

FIGS. 6A-6C show a side view, a longitudinal section through a motorhead, and a plan view from above, respectively, of a brush box for a DCmotor according to a third embodiment of the invention, which isdistinguished by a large number of additional power-improving measures;and

FIGS. 7A and 7B show the design and arrangement of the brushes in themotor head according to FIG. 6, in a dismantled state and in anassembled state, respectively.

DETAILED DESCRIPTION OF THE INVENTION

As already mentioned, measures are taken according to the invention fora DC motor with a commutator and brushes, which result in a brakingforce (friction) automatically impeding the process of the brusheslifting off the commutator when the brushes are forced away by thecommutator segments, and which at the same time allows the brushes toautomatically slide back without any impediment in the direction of thecommutator segments as soon as the process of the brushes being forcedaway has ended.

In order to achieve this, the brush boxes of the brushes must bepositioned at an angle to the (radial) normal to the relevant commutatorsegment, that is to say the brush boxes are no longer positioned atright angles to the relevant commutator segment.

Thanks to the angled position of the brush boxes, the pressure from thecommutator segments on the brushes results in a powerful pressurecontact in the vicinity of the commutator between the brush box and thebrush located in it. If the brush box is composed of an electricallyhighly conductive material (for example metal, in particular copper) andif the brush box is conductively connected to a corresponding currentconnecting pole for supplying current, a major proportion of the currentis passed via the highly conductive brush box to the brush in thevicinity of the commutator. This ensures a low resistance for thecurrent which is passed to the commutator.

Thanks to the angled positions of the brush boxes, the force which thecommutator exerts on the brush pushing it away is split into twovectors. One vector forces the brush against the wall of the box andthus increases the friction between the brush and the wall or the two ormore walls, while the other vector lies in the direction of thelongitudinal axis of the box and thus results in the movement of thebrush in the box. Owing to the wall friction, the first vector leads toconstraint of the longitudinal movement and to partial destruction ofthe movement energy. This reduces the extent to which the brushes arelifted off the commutator. When the pressure from the commutator ceases,the brush is pressed back against the commutator by the pressure spring,but now without any damping, in order to carry the current again,immediately.

Thanks to the angled position of the brush boxes and the movementconstraint associated with it, this also counteracts the radialmovements of the rotor, which are thus reduced. In consequence, therotor rotates more roundly overall.

FIGS. 2A and 2B show a DC motor according to a first embodiment of theinvention, with FIG. 2A showing a longitudinal section through the motorand FIG. 2B showing a plan view in the direction of the axis. The sameparts are in this case provided with the same reference symbols as inFIGS. 1A and 1B. FIG. 3 shows an enlarged detailed view of one of thebrushes from FIG. 2A.

The DC motor illustrated in FIGS. 2A and 2B differs from the known motorshown in FIGS. 1A and 1B by the arrangement of the brushes 32, 33relative to the (unchanged) commutator 14. The brushes 32, 33 areoriented with their associated brush boxes 34 obliquely outwards, sothat their movement direction 39 (double-headed arrow in FIG. 3), whichis predetermined by the brush boxes 34 and is the same as the directionof the force vector C in the force parallelogram shown in FIG. 3,includes an angle α (alpha) with the radial direction with respect tothe axis 29, which is at the same time the direction of the normal tothe commutator 14 (dashed line in the force parallelogram in FIG. 3),with this angle α being between 15° and 75°, and preferably about 45°.The two mutually opposite brushes 32, 33 in this case lie—as can be seenfrom FIG. 2B-on a common plane which passes through the axis 29. Theycan be transferred to one another by rotation through 180° about theaxis 29 (rotational symmetry).

The brushes 32, 33 are pressed obliquely against the commutator segments20 of the commutator 14 by appropriate pressure springs (spiral springsin the illustrated example) 37. The pressure springs 37 are secured inthe brush boxes 34 by appropriate spring locks 38. The brushes 32, 33are electrically connected by means of current carrying braids 35 to thecurrent connecting poles 36. The oblique position of the brush boxes 34and hence of the movement direction 39 allows the radial force A, whichis exerted on the brush 32 by the commutator 14, to be resolved inaccordance with the force parallelogram into a force C which actsparallel to the movement direction 39 and a force B which acts at rightangles to the movement direction 39. This force B which acts at rightangles to the wall of the brush box 34 presses the brush 32 against thewall, and thus increases the friction between the brush box 34 and thebrush 32 when the brush is moving in the movement direction 39. Thiscauses friction damping, which brakes and damps the process of thebrushes lifting off the commutator 14. When the radial force Adecreases, the brush 32 is pushed by the pressure spring 37 in thedirection of the commutator 14 parallel to the movement direction 39,with the brush 32 being able to slide freely in the brush box 34 withoutbeing subject to any particular friction or other damping. The distanceand hence the time as well for which the brush is lifted off thecommutator 14 are thus reduced, thus increasing the power of the motor.

As soon as the brushes 32, 33 make contact with the commutator 14 onceagain, particularly when the brush boxes 34 are conductively connectedto the appropriate current connecting poles 36, the current is passedthrough the lower part of the brush boxes 34 to the lower end of thebrushes, close to the commutator. The current flows through theelectrically highly conductive box walls more directly and with lessresistance to the commutator 14. This also increases the power of themotor.

FIGS. 4A and 4B show a DC motor 40 according to a second embodiment ofthe invention, with FIG. 4A showing a longitudinal section through themotor and FIG. 4B showing a plan view in the axial direction. The sameparts are in this case provided with the same reference symbols as inFIGS. 1A and 1B. FIG. 5 shows an enlarged detailed view of one of thebrushes from FIG. 4B.

As can be seen from FIG. 4B, the brush boxes 44 for the brushes 42, 43no longer lie on a common plane which passes through the axis 29, but ona common plane which is at right angles to the axis 29 (see FIG. 4A).The oblique position of the movement direction 41 (FIG. 5) relative tothe radial direction (the dashed line in the force parallelogram in FIG.5) is in this case achieved by the two brushes 42, 43 being arrangedlaterally offset parallel in the opposite direction from the positionshown in FIG. 1B. This also results in a tilt angle α, which leads tothe radial force A being resolved into two mutually perpendicular forcesB and C, which lead to the damping, according to the invention, of thelifting-off movement, while the return movement of the brushes is incontrast not influenced. In this situation as well, the angle α is inthe range between 15° and 75°, preferably about 45°. This likewiseresults in the reduction of the electrical resistance for the currentwhich is passed to the commutator 14. The brushes 42, 43 are connectedin the same way via current carrying braids 45 to the current connectingpoles 46. In this case, torque springs are used as the pressure springs47. At the same time, the brush boxes 44 are conductively connected tothe corresponding current connecting poles 46.

On the basis of the brush configuration that is shown in FIGS. 2A and2B, in which the longitudinal axes of the brushes 32, 33 include anangle of about 45° with the axis 29 of the motor and lie on a commonplane with the axis 29, further improvements with respect to the motorpower and the thermal design of the motor can be achieved despite thehighly constrained spatial conditions by using a motor head with brushboxes and brushes according to the exemplary embodiment shown in FIGS.6A-6C and FIGS. 7A and 7B.

The motor head 48 shown in FIGS. 6A-6C is in the form of a shell and,for reasons of good thermal conductivity, is composed of aluminium andis provided on the outside with a number of cooling ribs 49, which arein the form of rings that are concentric about the axis 29. The coolingribs 49 enlarge the heat transmission area between the motor head 48 andthe surrounding air in a manner which is know per se.

A hole runs in the axial direction in the centre of the motor head 48and holds a ball bearing 55 to provide the bearing for the central shaft58 of the rotor. The ball bearing 55 is itself borne elastically in theradial and axial directions in the motor head 48 in order to allowautomatically adjusting precise bearing at high rotation speeds of up to60 000 rpm, and to minimize the brushes being knocked away as a resultof non-round running. Two O rings 56, 57 are used for the elasticbearing (FIG. 6B). The one O ring 56 is seated in the axial directionbetween the ball bearing 55 and an undercut in the central hole in themotor head. This means that the ball bearing 55 can be supportedelastically on the undercut in the axial direction. The other O ring 57surrounds the outer shell of the ball bearing 55 concentrically, thusallowing the ball bearing to be borne elastically in the hole.

Oblique holes are provided in a corresponding manner in the motor head48 in order to hold the tubular brush boxes 50, 51. The inner walls ofthese holes are anodized and thus form a thin electrical insulationlayer, which electrically isolates the brush boxes 50, 51, which areinserted into the holes, from the motor head 48, but withoutsignificantly adversely affecting the good thermal contact between thebrush boxes 50, 51 and the motor head 48. This ensures that the brushboxes 50, 51 can be used to supply current to the brushes (63 in FIGS.7A and 7B) and, at the same time, that heat which is absorbed from thebrushes can be emitted effectively to the motor head 48 and from therevia the cooling ribs 49 to the environment. The lower ends of the brushboxes 50, 51 also continue to a point quite close to the commutator 59.This ensures that, on the one hand, current is passed with lowresistance via the brush boxes 50, 51 to the tips of the brushes 63, andon the other hand that heat is dissipated directly from the tips of thebrushes 63 to the motor head 48.

A further effective measure for cooling the commutator 59 and the motorhead 48, in which temperatures of up to 100° C. may occur during racingoperation, are ventilation channels 66 (FIG. 6A) which are milled in themotor head 48, run in a helical line and connect the interior of themotor head 48 to the environment. The rotation sense of the helicallines from the outside inwards in this case corresponds to the rotationdirection of the motor. Cooling air can be sucked through theventilation channels 66 from the outside into the interior of the motorhead 48, can flow axially through the motor, and can emerge again on theopposite end face of the motor. Sucking air in in a simple manner makesit possible for the winding connections (18 in FIG. 2A) of the windings(13 in FIG. 2A) which are connected to the commutator 59 to be bent suchthat they act as fan vanes when the motor is running in the normaldirection, forcing the air through windings in the axial direction.

Novel precautions are likewise taken on the electrical side in order topass the current to the commutator 59 with the losses being as low aspossible. In conventional racing motors, the brush boxes areconductively connected to two connecting lugs which are arrangedphysically separately and are used for connection of the actual powersupply cable and for a regulator line. The current carrying braids (64in FIG. 7A) which are embedded in the brushes are soldered on at a thirdpoint. This results in relatively long conduction paths, which have adisadvantageous effect at the high current levels that occur. In theexemplary embodiment shown in FIGS. 6A-6C and 7A-7B, in contrast, allthe electrical cables for each pole (the power supply cable, theregulator line and the current carrying braids) are connected to therespectively brush box directly at a single point in order to produceshort distances. For this purpose, each of the brush boxes 50, 51 isprovided with an annular flange 54 (see also FIG. 6C), to which thelines and cables are firmly soldered, directly adjacent to the pointwhere the brush box emerges from the motor head 48 to be outside. Inorder to allow the lines and cables to be soldered individually to theflange 54 without any difficulties, the flange 54 has a preciselydefined thickness and is subdivided into individual sectors 68, whichare thermally decoupled from one another.

By virtue of the design, the current is at each pole advantageouslypassed over three different paths to the tip of the brush, specifically(i) via the current carrying braid 64 and the brush 63, (ii) via thebrush box 50, 51, and (iii) via the pressure spring 65 and the brush 63.

In order to make it easier to install the brushes, which have to bereplaced relatively frequently owing to the high degree of wear duringracing operation, the brush boxes 50, 51 and the pressure springs 65 aredesigned in a specific manner in the exemplary embodiment shown in FIGS.6A-6C and 7A-7B. A (widened) section 62 with an enlarged internaldiameter is arranged in front of the outer end of the brush box 50, 51.The widened area forms an undercut in the brush box 50, 51, on which theouter end of the pressure spring 65 can be supported. In order to allowthe pressure spring 65 to be inserted into the brush box 50, 51 from theoutside, and to latch it behind the undercut, without any difficulties,it is designed such that it runs slightly conically inwards. The conicalshape also prevents the pressure spring 65 from carrying out undesirableresonant oscillations. The pressure spring 65 is advantageously made ofINOX wire, so that the spring constant remains largely stable over thewide temperature range that occurs. As is shown in FIG. 7A, the brush 63is installed by pushing the pressure spring 65 over the current carryingbraid 64 until its front end abuts against the brush 63. The brush 63and the pressure spring 65 are then inserted into the brush box 50 untilthe outer end of the pressure spring 65 latches in on the undercut ofthe section 62 (FIG. 7B). Finally, the current carrying braid 64 ispassed outwards through a slot 52 which is arranged at the outer end ofthe brush box 50, is wound a number of times around the brush box 50underneath a collar 53 for strain relief, and is then firmly soldered tothe flange 54.

The internal area which is made available by the shell-like motor head48 can be used to accommodate means for suppression of the motor in aspace-saving manner. The suppression means, which comprise capacitors,are arranged on a printed circuit board 62, which surrounds thecommutator 59 in a semicircular shape. The suppression circuit iselectrically connected directly via suitably bent contact springs 60,which are pushed over the edge of the circuit board 61, and pressdirectly against the brush boxes 50, 51 such that they make contact(FIG. 6B). An externally visible light-emitting diode (LED) 67 may alsobe provided on the circuit board 61, with this light-emitting diode 67being used to check the rotation direction and illuminating only whenthe motor is connected in the correct polarity. All of the components onthe circuit board 61 are preferably in the form of SMD elements, forspace reasons.

Overall, the invention is distinguished by the following characteristicsand advantages:

Owing to the angled position of the brush boxes, the pressure of thecommutator segments on the brushes results in a powerful contact betweenthe brush box and the brush all the way down to the commutator. Some ofthe current is thus passed via the highly conductive brush box to thebrush in the vicinity of the commutator, thus reducing the resistance.

Thanks to the angled position of the brush boxes, the force which thecommutator may exert on the brush pushing it away is resolved into twovectors. One vector pushes the brush against at least one wall of thebox, in which the brush can move corresponding to the second vector(longitudinal direction of the carbon). The friction on the walldestroys some of the energy. This makes it harder for the brushes tolift off the commutator. When the pressure from the commutator ceases,then the brush is pushed against the commutator without any damping bythe normal pressure spring, in order to carry the current immediately.

The angled position of the brush boxes counteracts the radial movementsof the rotor; these movements are kept small so that the commutator runsmore roundly.

It is advantageous that no additional moving parts are required. Themass of the brushes must be kept as low as possible in order to keep theinertia torque low. For example, hydraulic shock absorbers areunsuitable since the weight of the moving parts would make the resultsworse.

The optimum position angle for the brushes may be defined to be 45°±30°.

The intensity of the damping can be adjusted by means of the positionangle.

If positioned at right angles (the brush boxes are at right angles tothe commutator segment; α=0), the damping is zero. The greater thepositioning angle that is set, the greater is the damping.

1-25. (cancelled)
 26. A DC motor comprising: a rotor mounted in ahousing for rotation about an axis, the rotor having at least onewinding for receiving direct current applied in alternating directionsvia a commutator which is arranged on the rotor, the commutator havingtwo or more electrically conductive commutator segments located on acylindrical casing about the axis; brushes seated on the commutator, thebrushes being mounted for movement relative to the commutator and beingpushed by spring pressure onto the commutator; and means for damping themovement of the brushes against the spring pressure and for allowingsubstantially unimpeded movement of the brushes with the springpressure.
 27. The DC motor of claim 26, wherein the means for dampingand allowing includes brush boxes, with each brush box configured toreceive at least one brush such that it can slide in a movementdirection determined by the brush box that deviates from a radialdirection with respect to the axis in such a way that the brush issubjected to increased sliding friction on at least one wall of thebrush box during movement against the spring pressure caused by thecommutator.
 28. The DC motor of claim 27, wherein the movement directionis an angle between 15° and 75° to the radial direction with respect tothe axis.
 29. The DC motor of claim 28, wherein the angle is about 45°.30. The DC motor of claim 27, wherein the movement direction lies on acommon plane which passes through the axis.
 31. The DC motor of claim30, wherein the movement direction is aligned obliquely outwards. 32.The DC motor of claim 27, wherein the movement direction lies on acommon plane which is at right angles to the axis.
 33. The DC motor ofclaim 27, wherein two brushes are provided and are arranged with respectto one another such that they can be transferred into one another byrotation through 180° about the axis of the DC motor.
 34. The DC motorof claim 27, wherein walls of each brush box are made from anelectrically conductive material and each brush box is connected tomeans for supplying electrical current.
 35. The DC motor of claim 34,wherein the walls of each brush box are made of copper.
 36. The DC motorof claim 27, wherein each brush box and each brush have a circular crosssection.
 37. The DC motor of claim 34, wherein each brush box isarranged in a motor head in the form of a shell, the motor head is madeof a thermally conductive material and each brush box is mounted in anelectrically isolated manner in the motor head.
 38. The DC motor ofclaim 37, wherein the motor head is made from aluminium, and the brushboxes are electrically isolated from the motor head by an anodizedintermediate layer.
 39. The DC motor of claim 37, wherein the motor headhas cooling ribs on an outer face thereof.
 40. The DC motor of claim 39,wherein the cooling ribs are formed concentrically with respect to theaxis.
 41. The DC motor of claim 37, wherein ventilation channels areprovided in the motor head for supplying cooling air to an interior ofthe DC motor.
 42. The DC motor of claim 41, wherein the winding iselectrically connected via winding connections to the commutator, andthe winding connections are configured to act as fan vanes when themotor is running in a normal direction for urging cooling air throughthe ventilation channels.
 43. The DC motor of claim 41, wherein theventilation channels are in the form of helical lines.
 44. The DC motorof claim 26, wherein the rotor is supported at an end thereof where thecommutator is located by a ball bearing such that the rotor can rotate,and the ball bearing is elastically mounted.
 45. The DC motor of claim44, wherein the ball bearing is mounted elastically in the radial andaxial directions, and the elastic bearing is produced by means of Orings which concentrically surround the ball bearing.
 46. The DC motorof claim 27, wherein pressure springs in the form of spiral springswhich taper conically towards the brushes are provided in order toproduce the spring pressure on the brushes, the pressure springs aresupported by their ends facing away from the brushes on an undercut inthe brush boxes, and the pressure springs are made of INOX wire.
 47. TheDC motor of claim 34, wherein each brush box includes means forelectrically connecting lines coming from the outside to a correspondingpole.
 48. The DC motor of claim 47, wherein the means for electricallyconnecting includes a flange which surrounds the brush box and which issubdivided into two or more sectors.
 49. The DC motor of claim 37,wherein a printed circuit board is arranged in the interior of the motorhead, the printed circuit board includes a circuit for motorsuppression, and the circuit board is electrically connected to thebrush boxes via contact springs which press against the brush boxes. 50.The DC motor of claim 49, wherein an externally visible light-emittingdiode is arranged on the circuit board.
 51. A motor head (or endbell)for a DC motor having a rotor with a commutator and a motor axis, saidmotor head comprising: brushes to be seated on the commutator, thebrushes being mounted for movement relative to the commutator and beingpushed by spring pressure onto the commutator; and brush boxes, witheach brush box configured to receive at least one brush such that it canslide in a movement direction determined by the brush box, wherein themotor head is made of a material of good thermal conductivity and eachbrush box is mounted in an electrically isolated manner in the motorhead.
 52. The motor head of claim 51, wherein the motor head is made ofa metal.
 53. The motor head of claim 52, wherein the motor head is madefrom aluminum, and the brush boxes are electrically isolated from themotor head by an anodized intermediate layer.
 54. The motor head ofclaim 51, wherein the motor head has cooling ribs on an outer facethereof, and the cooling ribs are formed concentrically with respect tothe axis.
 55. The motor head of claim 51, wherein the motor head has theform of a shell.
 56. The motor head of claim 55, wherein a printedcircuit board is arranged in the interior of the motor head, the printedcircuit board includes a circuit for motor suppression, the circuitboard is electrically connected to the brush boxes via contact springswhich press against the brush boxes, and an externally visiblelight-emitting diode is arranged on the circuit board.
 57. The motorhead of claim 51, wherein the movement direction is an angle between 15°and 75° to the radial direction with respect to the axis.
 58. The motorhead of claim 51, comprising a ball bearing for rotatably supporting therotor at an end thereof where the commutator is located, wherein theball bearing is elastically mounted.
 59. The motor head of claim 58,wherein the ball bearing is mounted elastically in the radial and axialdirections, and the elastic mounting is achieved by means of O ringswhich concentrically surround the ball bearing and support the ballbearing in axial direction.
 60. The motor head of claim 51, whereinpressure springs in the form of spiral springs which taper conicallytowards the brushes are provided in order to produce the spring pressureon the brushes, the pressure springs are supported by their ends facingaway from the brushes on an undercut in the brush boxes, and thepressure springs are made of INOX wire.
 61. The motor head of claim 51,wherein each brush box includes means for electrically connecting linescoming from the outside to a corresponding pole.
 62. The motor head ofclaim 61, wherein the means for electrically connecting includes aflange which surrounds the brush box and which is subdivided into two ormore sectors.
 63. The motor head of claim 51, wherein each brush box andeach brush have a circular cross section, and the walls of each brushbox are made of copper.
 64. A motor head (or endbell) for a DC motorhaving a rotor with a commutator and a motor axis, said motor headcomprising: brushes to be seated on the commutator, the brushes beingmounted for movement relative to the commutator and being pushed byspring pressure onto the commutator; and brush boxes, with each brushbox configured to receive at least one brush such that it can slide in amovement direction determined by the brush box, wherein the movementdirection is an angle between 15° and 75° to the radial direction withrespect to the axis.
 65. The motor head of claim 64, wherein the motorhead is made of a material of good thermal conductivity and each brushbox is mounted in an electrically isolated manner in the motor head. 66.The motor head of claim 65, wherein the motor head is made of a metal.67. The motor head of claim 66, wherein the motor head is made fromaluminum, and the brush boxes are electrically isolated from the motorhead by an anodized intermediate layer.
 68. The motor head of claim 66,wherein the motor head has cooling ribs on an outer face thereof, andthe cooling ribs are formed concentrically with respect to the axis. 69.The motor head of claim 64, wherein the motor head has the form of ashell.
 70. The motor head of claim 69, wherein a printed circuit boardis arranged in the interior of the motor head, the printed circuit boardincludes a circuit for motor suppression, the circuit board iselectrically connected to the brush boxes via contact springs whichpress against the brush boxes, and an externally visible light-emittingdiode is arranged on the circuit board.
 71. The motor head of claim 64,comprising a ball bearing for rotatably supporting the rotor at an endthereof where the commutator is located, wherein the ball bearing iselastically mounted.
 72. The motor head of claim 71, wherein the ballbearing is mounted elastically in the radial and axial directions, andthe elastic mounting is achieved by means of O rings whichconcentrically surround the ball bearing and support the ball bearing inaxial direction.
 73. The motor head of claim 64, wherein pressuresprings in the form of spiral springs which taper conically towards thebrushes are provided in order to produce the spring pressure on thebrushes, the pressure springs are supported by their ends facing awayfrom the brushes on an undercut in the brush boxes, and the pressuresprings are made of INOX wire.
 74. The motor head of claim 64, whereineach brush box includes means for electrically connecting lines comingfrom the outside to a corresponding pole.
 75. The motor head of claim74, wherein the means for electrically connecting includes a flangewhich surrounds the brush box and which is subdivided into two or moresectors.
 76. The motor head of claim 64, wherein each brush box and eachbrush have a circular cross section, and the walls of each brush box aremade of copper.
 77. A DC motor comprising: a rotor mounted in a housingfor rotation about an axis, the rotor having at least one winding forreceiving direct current applied in alternating directions via acommutator which is arranged on the rotor, the commutator having two ormore electrically conductive commutator segments located on acylindrical casing about the axis; and brushes seated on the commutator,the brushes being mounted for movement relative to the commutator andbeing pushed by spring pressure onto the commutator, wherein the rotoris supported at an end thereof where the commutator is located bybearing means such that the rotor can rotate and the bearing means iselastically mounted.
 78. The DC motor of claim 77, wherein the bearingmeans comprises a ball bearing.
 79. The DC motor of claim 77, whereinthe bearing means is mounted elastically in the radial and axialdirections by means of O-rings which concentrically surround the bearingmeans.
 80. The DC motor of claim 77, wherein the bearing means ismounted in a motor head.
 81. The DC motor of claim 80, wherein the motorhead is made of a material of high thermal conductivity.
 82. The DCmotor of claim 80, wherein the motor head is made of aluminum.
 83. Amotor head for a DC motor having a rotor with a commutator and a motoraxis, said motor head comprising: brushes to be seated on thecommutator, the brushes being mounted for movement relative to thecommutator and being pushed by spring pressure onto the commutator; andbrush boxes, with each brush box configured to receive at least onebrush such that it can slide in a movement direction determined by thebrush box, wherein an electric circuit for motor suppression is arrangedon the motor head and the electric circuit is electrically connected tothe brushes.
 84. The motor head of claim 83, wherein the circuit isarranged in an interior of the motor head.
 85. The motor head of claim83, wherein the electric circuit comprises one or more capacitors. 86.The motor head of claim 83, wherein the electric circuit is arranged ona printed circuit board and is electrically connected to the brushes viacontact springs which press against the brush boxes.
 87. A motor headfor a DC motor having a rotor with a commutator and a motor axis, saidmotor head comprising: brushes seated on the commutator, the brushesbeing mounted for movement relative to the commutator and being pushedby spring pressure onto the commutator; and an electric circuit with anexternally visible light-emitting diode arranged on the motor head. 88.The motor head of claim 87, wherein the electric circuit is arranged inthe interior of the motor head.
 89. The motor head of claim 88, whereinthe electric circuit is arranged on a printed circuit board and iselectrically connected to the brushes via contact springs which pressagainst the brush boxes.
 90. The motor head of claim 87, wherein thelight-emitting diode is used to check the rotation direction and is onlyilluminating when the motor is connected in the correct polarity.